diff --git a/package.json b/package.json
index ce27e172..7db9eea7 100644
--- a/package.json
+++ b/package.json
@@ -56,7 +56,7 @@
     "sass": "^1.16.1",
     "source-map-support": "^0.5.10",
     "ts-jest": "^27.0.5",
-    "typescript": "3.9.6",
+    "typescript": "4.5.2",
     "uglify-es": "^3.3.9"
   },
   "jest": {
diff --git a/src/component/component.ts b/src/component/component.ts
index e5726ff0..b3c48f3a 100644
--- a/src/component/component.ts
+++ b/src/component/component.ts
@@ -8,6 +8,7 @@ import type { ComponentNode } from "./component_node";
 export class Component {
   static template: string = "";
   static style: string = "";
+  static props?: any;
 
   props: any;
   env: Env;
diff --git a/src/component/props_validation.ts b/src/component/props_validation.ts
index 223f5ffa..5aebdd62 100644
--- a/src/component/props_validation.ts
+++ b/src/component/props_validation.ts
@@ -26,26 +26,23 @@ export function applyDefaultProps(props: { [key: string]: any }, ComponentClass:
  * visit recursively the props and all the children to check if they are valid.
  * This is why it is only done in 'dev' mode.
  */
-
-// message: { type: String, default: "hello" };
-
 export const validateProps = function (name: string | typeof Component, props: any, parent?: any) {
-  const ComponentClass =
-    typeof name !== "string" ? name : parent.constructor.components[name as string];
+  const ComponentClass = (
+    typeof name !== "string" ? name : parent.constructor.components[name]
+  ) as typeof Component;
 
   applyDefaultProps(props, ComponentClass);
 
-  const propsDef = (<any>ComponentClass).props;
+  const propsDef = ComponentClass.props;
   if (propsDef instanceof Array) {
     // list of strings (prop names)
-    for (let i = 0, l = propsDef.length; i < l; i++) {
-      const propName = propsDef[i];
+    for (const propName of propsDef) {
       if (propName[propName.length - 1] === "?") {
         // optional prop
         break;
       }
       if (!(propName in props)) {
-        throw new Error(`Missing props '${propsDef[i]}' (component '${ComponentClass.name}')`);
+        throw new Error(`Missing props '${propName}' (component '${ComponentClass.name}')`);
       }
     }
     for (let key in props) {
@@ -67,7 +64,9 @@ export const validateProps = function (name: string | typeof Component, props: a
       try {
         isValid = isValidProp(props[propName], propsDef[propName]);
       } catch (e) {
-        e.message = `Invalid prop '${propName}' in component ${ComponentClass.name} (${e.message})`;
+        (e as Error).message = `Invalid prop '${propName}' in component ${ComponentClass.name} (${
+          (e as Error).message
+        })`;
         throw e;
       }
       if (!isValid) {
diff --git a/tests/components/basics.test.ts b/tests/components/basics.test.ts
index 609f07b6..7d3784f8 100644
--- a/tests/components/basics.test.ts
+++ b/tests/components/basics.test.ts
@@ -40,14 +40,14 @@ describe("basics", () => {
     class SomeWidget extends Component {
       static template = xml`<div>content</div>`;
     }
-    let error;
+    let error: Error;
     try {
       await mount(SomeWidget, document.createDocumentFragment() as any);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Cannot mount component: the target is not a valid DOM element");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Cannot mount component: the target is not a valid DOM element");
   });
 
   test("can mount a simple component with props", async () => {
@@ -160,28 +160,28 @@ describe("basics", () => {
       static template = xml`<span>simple vnode</span>`;
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(Test, null as any);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Cannot mount component: the target is not a valid DOM element");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Cannot mount component: the target is not a valid DOM element");
   });
 
   test("a component cannot be mounted in a detached node", async () => {
     class Test extends Component {
       static template = xml`<div/>`;
     }
-    let error;
+    let error: Error;
     try {
       await mount(Test, document.createElement("div"));
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Cannot mount a component on a detached dom node");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Cannot mount a component on a detached dom node");
   });
 
   test("crashes if it cannot find a template", async () => {
@@ -189,14 +189,14 @@ describe("basics", () => {
       static template = "wrongtemplate";
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(Test, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe('Missing template: "wrongtemplate"');
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe('Missing template: "wrongtemplate"');
   });
 
   test("class component with dynamic text", async () => {
diff --git a/tests/components/error_handling.test.ts b/tests/components/error_handling.test.ts
index 5f24d5e9..45816181 100644
--- a/tests/components/error_handling.test.ts
+++ b/tests/components/error_handling.test.ts
@@ -35,18 +35,18 @@ describe("basics", () => {
     expect(fixture.innerHTML).toBe("<div><div>heyfalse</div></div>");
     parent.state.flag = true;
 
-    let error;
+    let error: Error;
     try {
       await parent.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
     expect(fixture.innerHTML).toBe("");
     expect(status(parent)).toBe("destroyed");
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'this'\)|Cannot read property 'this' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
   });
 
   test("display a nice error if it cannot find component", async () => {
@@ -58,14 +58,14 @@ describe("basics", () => {
       static template = xml`<SomeMispelledComponent />`;
       static components = { SomeComponent };
     }
-    let error;
+    let error: Error;
     try {
       await mount(Parent, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe('Cannot find the definition of component "SomeMispelledComponent"');
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe('Cannot find the definition of component "SomeMispelledComponent"');
     expect(console.error).toBeCalledTimes(0);
     console.error = consoleError;
   });
@@ -108,16 +108,16 @@ describe("errors and promises", () => {
       static template = xml`<div><t t-esc="this.will.crash"/></div>`;
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(App, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'crash'\)|Cannot read property 'crash' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
 
     expect(console.error).toBeCalledTimes(0);
     console.error = consoleError;
@@ -136,14 +136,14 @@ describe("errors and promises", () => {
       }
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(App, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("boom");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("boom");
     expect(fixture.innerHTML).toBe("");
 
     expect(console.error).toBeCalledTimes(0);
@@ -166,14 +166,14 @@ describe("errors and promises", () => {
 
     const app = await mount(App, fixture);
     app.val = 4;
-    let error;
+    let error: Error;
     try {
       await app.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("boom");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("boom");
     expect(fixture.innerHTML).toBe("");
 
     expect(console.error).toBeCalledTimes(0);
@@ -196,14 +196,14 @@ describe("errors and promises", () => {
 
     const app = await mount(App, fixture);
     app.val = 4;
-    let error;
+    let error: Error;
     try {
       await app.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("boom");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("boom");
     expect(fixture.innerHTML).toBe("");
 
     expect(console.error).toBeCalledTimes(0);
@@ -222,16 +222,16 @@ describe("errors and promises", () => {
       static components = { Child };
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(App, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'crash'\)|Cannot read property 'crash' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
 
     expect(console.error).toBeCalledTimes(0);
     console.error = consoleError;
@@ -249,16 +249,16 @@ describe("errors and promises", () => {
     const app = await mount(App, fixture);
     expect(fixture.innerHTML).toBe("<div></div>");
     app.flag = true;
-    let error;
+    let error: Error;
     try {
       await app.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'crash'\)|Cannot read property 'crash' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
 
     expect(console.error).toBeCalledTimes(0);
     console.error = consoleError;
@@ -273,20 +273,20 @@ describe("errors and promises", () => {
       static components = { Child };
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(Parent, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'y'\)|Cannot read property 'y' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
   });
 
   test("errors in mounted and in willUnmount", async () => {
-    expect.assertions(2); // apparently this expect count in assertions...
+    expect.assertions(2);
     class Example extends Component {
       static template = xml`<div/>`;
       val: any;
@@ -305,7 +305,7 @@ describe("errors and promises", () => {
     try {
       await mount(Example, fixture);
     } catch (e) {
-      expect(e.message).toBe("Error in mounted");
+      expect((e as Error).message).toBe("Error in mounted");
     }
   });
 });
diff --git a/tests/components/props_validation.test.ts b/tests/components/props_validation.test.ts
index c6a260a5..c1df7ba5 100644
--- a/tests/components/props_validation.test.ts
+++ b/tests/components/props_validation.test.ts
@@ -46,23 +46,23 @@ describe("props validation", () => {
       static components = { SubComp };
       static template = xml`<div><SubComp /></div>`;
     }
-    let error;
+    let error: Error | undefined;
 
     try {
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(`Missing props 'message' (component 'SubComp')`);
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(`Missing props 'message' (component 'SubComp')`);
     error = undefined;
 
     try {
       await mountApp(Parent, false);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
   });
 
   test("props: list of strings", async () => {
@@ -75,14 +75,14 @@ describe("props validation", () => {
       static template = xml`<div><SubComp /></div>`;
     }
 
-    let error;
+    let error: Error;
     try {
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(`Missing props 'message' (component 'SubComp')`);
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(`Missing props 'message' (component 'SubComp')`);
   });
 
   test("validate simple types", async () => {
@@ -108,32 +108,32 @@ describe("props validation", () => {
       };
       (Parent as any).components = { SubComp };
 
-      let error;
+      let error: Error | undefined;
       props = {};
 
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeDefined();
-      expect(error.message).toBe(`Missing props 'p' (component '_a')`);
+      expect(error!).toBeDefined();
+      expect(error!.message).toBe(`Missing props 'p' (component '_a')`);
       error = undefined;
       props = { p: test.ok };
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeUndefined();
+      expect(error!).toBeUndefined();
       props = { p: test.ko };
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeDefined();
-      expect(error.message).toBe("Invalid Prop 'p' in component '_a'");
+      expect(error!).toBeDefined();
+      expect(error!.message).toBe("Invalid Prop 'p' in component '_a'");
     }
   });
 
@@ -159,31 +159,31 @@ describe("props validation", () => {
         static template = xml`<div>hey</div>`;
       };
       (Parent as any).components = { SubComp };
-      let error;
+      let error: Error | undefined;
       props = {};
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeDefined();
-      expect(error.message).toBe(`Missing props 'p' (component '_a')`);
+      expect(error!).toBeDefined();
+      expect(error!.message).toBe(`Missing props 'p' (component '_a')`);
       error = undefined;
       props = { p: test.ok };
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeUndefined();
+      expect(error!).toBeUndefined();
       props = { p: test.ko };
       try {
         await mountApp(Parent);
       } catch (e) {
-        error = e;
+        error = e as Error;
       }
-      expect(error).toBeDefined();
-      expect(error.message).toBe("Invalid Prop 'p' in component '_a'");
+      expect(error!).toBeDefined();
+      expect(error!.message).toBe("Invalid Prop 'p' in component '_a'");
     }
   });
 
@@ -199,30 +199,30 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error;
     let props: { p?: any };
     try {
       props = { p: "string" };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: true };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: 1 };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
   });
 
   test("can validate an optional props", async () => {
@@ -237,30 +237,30 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error;
     let props: { p?: any };
     try {
       props = { p: "key" };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = {};
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: 1 };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
   });
 
   test("can validate an array with given primitive type", async () => {
@@ -275,35 +275,35 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error | undefined;
     let props: { p?: any };
     try {
       props = { p: [] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: ["string"] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: [1] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     error = undefined;
     try {
       props = { p: ["string", 1] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
   });
 
@@ -319,37 +319,37 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error;
     let props: { p?: any };
     try {
       props = { p: [] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: ["string"] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: [false, true, "string"] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: [true, 1] };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
   });
 
   test("can validate an object with simple shape", async () => {
@@ -366,40 +366,40 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error | undefined;
     let props: { p?: any };
     try {
       props = { p: { id: 1, url: "url" } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: { id: 1, url: "url", extra: true } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid prop 'p' in component SubComp (unknown prop 'extra')");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid prop 'p' in component SubComp (unknown prop 'extra')");
     try {
       props = { p: { id: "1", url: "url" } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
     error = undefined;
     try {
       props = { p: { id: 1 } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
   });
 
   test("can validate recursively complicated prop def", async () => {
@@ -422,30 +422,30 @@ describe("props validation", () => {
         return props.p;
       }
     }
-    let error;
+    let error: Error;
     let props: { p?: any };
     try {
       props = { p: { id: 1, url: true } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: { id: 1, url: [12] } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       props = { p: { id: 1, url: [12, true] } };
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'p' in component 'SubComp'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'p' in component 'SubComp'");
   });
 
   test("can validate optional attributes in nested sub props", () => {
@@ -462,20 +462,20 @@ describe("props validation", () => {
         },
       };
     }
-    let error;
+    let error: Error;
     try {
       validateProps(TestComponent as any, { myprop: [{}] });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       validateProps(TestComponent as any, { myprop: [{ a: 1 }] });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(
       "Invalid prop 'myprop' in component TestComponent (unknown prop 'a')"
     );
   });
@@ -488,20 +488,20 @@ describe("props validation", () => {
         },
       };
     }
-    let error;
+    let error: Error;
     try {
       validateProps(TestComponent as any, { size: "small" });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     try {
       validateProps(TestComponent as any, { size: "abcdef" });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'size' in component 'TestComponent'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'size' in component 'TestComponent'");
   });
 
   test("can validate with a custom validator, and a type", () => {
@@ -514,30 +514,30 @@ describe("props validation", () => {
         },
       };
     }
-    let error;
+    let error: Error | undefined;
     try {
       validateProps(TestComponent as any, { n: 3 });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeUndefined();
+    expect(error!).toBeUndefined();
     expect(validator).toBeCalledTimes(1);
     try {
       validateProps(TestComponent as any, { n: "str" });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'n' in component 'TestComponent'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'n' in component 'TestComponent'");
     expect(validator).toBeCalledTimes(1);
-    error = null;
+    error = undefined;
     try {
       validateProps(TestComponent as any, { n: 100 });
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Invalid Prop 'n' in component 'TestComponent'");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Invalid Prop 'n' in component 'TestComponent'");
     expect(validator).toBeCalledTimes(2);
   });
 
@@ -647,18 +647,18 @@ describe("props validation", () => {
       static template = xml`<div><SubComp/></div>`;
       static components = { SubComp };
     }
-    let error;
+    let error: Error;
     try {
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Missing props 'p' (component 'SubComp')");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Missing props 'p' (component 'SubComp')");
   });
 
   test("props are validated whenever component is updated", async () => {
-    let error;
+    let error: Error;
     class SubComp extends Component {
       static props = { p: { type: Number } };
       static template = xml`<div><t t-esc="props.p"/></div>`;
@@ -674,10 +674,10 @@ describe("props validation", () => {
       (app as any).root.component.state.p = undefined;
       await (app as any).root.component.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Missing props 'p' (component 'SubComp')");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Missing props 'p' (component 'SubComp')");
   });
 
   test("default values are applied before validating props at update", async () => {
@@ -712,14 +712,14 @@ describe("props validation", () => {
       static components = { Child };
       static template = xml`<div><Child/></div>`;
     }
-    let error;
+    let error: Error;
     try {
       await mountApp(Parent);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe("Missing props 'mandatory' (component 'Child')");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Missing props 'mandatory' (component 'Child')");
   });
 });
 
diff --git a/tests/components/style_class.test.ts b/tests/components/style_class.test.ts
index a6e61a04..8c1b3f9a 100644
--- a/tests/components/style_class.test.ts
+++ b/tests/components/style_class.test.ts
@@ -338,16 +338,16 @@ describe("style and class handling", () => {
       static template = xml`<Child class="'a'"/>`;
       static components = { Child };
     }
-    let error;
+    let error: Error;
     try {
       await mount(ParentWidget, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'crash'\)|Cannot read property 'crash' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
     expect(fixture.innerHTML).toBe("");
   });
 });
diff --git a/tests/components/style_tag.test.ts b/tests/components/style_tag.test.ts
index c60a5eef..cd3d72e4 100644
--- a/tests/components/style_tag.test.ts
+++ b/tests/components/style_tag.test.ts
@@ -87,14 +87,14 @@ describe("styles and component", () => {
       static template = xml`<div class="app">text</div>`;
       static style = `.app {color: red;}`;
     }
-    let error;
+    let error: Error;
     try {
       await mount(App, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(
       "Invalid css stylesheet for component 'App'. Did you forget to use the 'css' tag helper?"
     );
   });
diff --git a/tests/components/t_component.test.ts b/tests/components/t_component.test.ts
index 91e01663..7ae59a2f 100644
--- a/tests/components/t_component.test.ts
+++ b/tests/components/t_component.test.ts
@@ -205,14 +205,14 @@ describe("t-component", () => {
       static components = { Child };
       static template = xml`<div><div t-component="Child"/></div>`;
     }
-    let error;
+    let error: Error;
     try {
       await mount(Parent, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(
       `Directive 't-component' can only be used on <t> nodes (used on a <div>)`
     );
   });
diff --git a/tests/components/t_model.test.ts b/tests/components/t_model.test.ts
index c8be3d3a..3fde0493 100644
--- a/tests/components/t_model.test.ts
+++ b/tests/components/t_model.test.ts
@@ -57,14 +57,14 @@ describe("t-model directive", () => {
         </div>`;
       state = useState({ text: "" });
     }
-    let error;
+    let error: Error;
     try {
       await mount(SomeComponent, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(`Invalid t-model expression: "state" (it should be assignable)`);
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(`Invalid t-model expression: "state" (it should be assignable)`);
   });
 
   test("basic use, on another key in component", async () => {
diff --git a/tests/components/t_props.test.ts b/tests/components/t_props.test.ts
index 3de1acd9..ce78d09b 100644
--- a/tests/components/t_props.test.ts
+++ b/tests/components/t_props.test.ts
@@ -42,7 +42,7 @@ describe("t-props", () => {
         a: "first",
         b: "second",
       });
-      a = "third";
+      a? = "third";
     }
     const parent = await mount(Parent, fixture);
     expect(fixture.textContent).toBe("thirdsecond");
diff --git a/tests/misc/portal.test.ts b/tests/misc/portal.test.ts
index 0b753e0e..1804e353 100644
--- a/tests/misc/portal.test.ts
+++ b/tests/misc/portal.test.ts
@@ -160,15 +160,15 @@ describe("Portal", () => {
             </div>`;
     }
 
-    let error;
+    let error: Error;
     try {
       await mount(Parent, fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
 
-    expect(error).toBeDefined();
-    expect(error.message).toBe("invalid portal target");
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("invalid portal target");
     expect(fixture.innerHTML).toBe(`<div></div>`);
   });
 
@@ -396,16 +396,16 @@ describe("Portal", () => {
     const parent = await mount(Parent, fixture);
     parent.state.error = true;
 
-    let error;
+    let error: Error;
     try {
       await parent.render();
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
+    expect(error!).toBeDefined();
     const regexp =
       /Cannot read properties of undefined \(reading 'crash'\)|Cannot read property 'crash' of undefined/g;
-    expect(error.message).toMatch(regexp);
+    expect(error!.message).toMatch(regexp);
   });
 
   test("portal's parent's env is not polluted", async () => {
@@ -519,16 +519,16 @@ describe("Portal: Props validation", () => {
           </Portal>
         </div>`;
     }
-    let error;
+    let error: Error;
     let app = new App(Parent);
     app.configure({ dev: true });
     try {
       await app.mount(fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(`Missing props 'target' (component 'Portal')`);
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(`Missing props 'target' (component 'Portal')`);
     console.info = consoleInfo;
   });
 
@@ -544,16 +544,16 @@ describe("Portal: Props validation", () => {
           </Portal>
         </div>`;
     }
-    let error;
+    let error: Error;
     let app = new App(Parent);
     app.configure({ dev: true });
     try {
       await app.mount(fixture);
     } catch (e) {
-      error = e;
+      error = e as Error;
     }
-    expect(error).toBeDefined();
-    expect(error.message).toBe(`Invalid Prop 'target' in component 'Portal'`);
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe(`Invalid Prop 'target' in component 'Portal'`);
     console.info = consoleInfo;
   });
 });